1. Field of the Invention
The present invention relates generally to wireless communications and more particularly to determination of a radio link quality state.
2. Description of the Related Art
In a wireless network, an asymmetric volume of data is typically exchanged between a base station and a mobile terminal. A mobile terminal usually transmits a fraction of the data on an uplink channel as compared to the data a base station transmits to the mobile on a downlink channel. To more efficiently use limited radio resources, a network may allocate uplink and downlink channels to match this expected asymmetric demand.
Additionally, a demand for downlink channel capacity may be intermittent. For example, a user surfing the Internet may transmit a few commands on the uplink to access a web page. Once the web page is available, the network transmits the web page data to the user on the downlink. Until the user selects the next link or goes to another web page, no user data is transferred.
Wireless systems often use one of two methods for transferring user data. Some wireless systems establish a link between a base station and a mobile station only after user data is received by the network and is waiting to be transferred to the user. Each time a new block of user data arrives, the system establishes a new connection between the base station and the mobile terminal then transfers the data. Once the data transfer is complete, in order to release the radio resource, the connection may be suspended and the channel becomes free for another data transfer. This scheme has the advantage that a data channel is not established when the channel would otherwise be idle. This efficient use of radio resources comes at the cost of increase data transfer latency. That is, an additional latency is added to each data transfer due to the time necessary to establish the link.
Alternatively, a wireless system may establish a dedicated channel between a base station and a mobile station. In such systems, a link is established prior to the arrival of user data and the latency of establishing a connection may be ignored from the time needed to transfer the user data. Typically, a dedicated channel remains idle until new data arrives for transfer to a mobile terminal. If a dedicated channel is established before user data arrives, a mobile terminal may monitor the dedicated channel to determine link quality prior to user data transfer. Unfortunately, such systems occupy at least one channel for each mobile terminal even though no data may be being transferred.
An example of a wireless network system specifying an established link prior to the availability of data for transfer is a High Speed Downlink Packet Access (HSDPA) network as defined by the Third Generation Partnership Project (3GPP). A 3GPP HSDPA system provides support for enhanced packet data services, which may heavily utilize a high-speed downlink shared channel (HS-DSCH). The 3GPP HSDPA recommendations specify an established associated dedicated physical channel (DPCH) in both uplink and downlink directions. Typically, a dedicated transport channel (DCH) is allocated a CDMA code and is mapped to a DPCH. Within a typical HSDPA system, the DCH is used to carry low-rate signalling and other background higher-layer data to the user—thereby higher rate data transfers make considerable use of the high-speed downlink shared channel (HS-DSCH).
When no user data or signaling information is available for transfer on the DCH, the DCH is largely unused, however, continues to occupy CDMA code resources on the downlink. A mobile terminal in an HSDPA system may monitor a downlink DCH to determine overall signal quality. The mobile terminal may then use the signal quality measurement to determine whether or not the mobile terminal is in data communication with the network. When downlink reception is determined to be unacceptably poor, the mobile terminal may attempt a re-establishment of the radio link, and may also release the radio resources used for uplink and cease their transmission.
Unfortunately, each dedicated channel occupies a resource, even when idle. In a CDMA system, each dedicated channel may be mapped to a unique CDMA code or set of codes allocated to that channel. In a CDMA system with a TDMA component, the code resource(s) may also apply for a predetermined period of time, or a timeslot. Since the available CDMA codes (and time slots, if applicable) are a finite resource in a CDMA system, each of these reserved but effectively unused codes in the aggregate derogates system performance and capacity. In such situations with a large number of established but idle links, a system may become code-limited.
It is therefore desirable to implement a wireless network for transferring intermittent user data that more efficiently uses code resources and improves system capacity. A method by which this may be achieved is by sending the higher-layer data and signaling to the user on the (intermittent) downlink shared channel, thereby alleviating the need for the downlink dedicated channel. However, means for determining downlink link quality and establishing a radio link quality state must continue to be provided in the absence of the downlink dedicated channel.